The present invention relates to a display device for displaying image data (including video data, static image data, and text data) and a display driver for driving display devices. More specifically, the present invention relates to display devices such as liquid crystal display devices, CRT (Cathode-Ray Tube) display devices, plasma display devices, EL (Electro Luminescence) display device, FE (Field Emission) display devices and the like and display drivers driving these display devices.
Recent years have seen the widespread digitizing of video and increased quality in the video signals themselves. There is a demand for displays that can provide high-quality displaying of static images and video. There are many types of displays that display video signals, with particular interest being placed on liquid crystal displays that are compact, low-power, low-flicker, and the like.
However, displaying video on conventional liquid crystal displays results in afterimages, leading to decreased image quality.
A method for improving image quality for displaying video in liquid crystal displays is presented in Japanese laid-open patent publication number Hei 10-39837. This publication describes a liquid crystal display device that includes: a display panel in which liquid crystal is interposed between an active matrix substrate and an opposing electrodes substrate; a driver circuit for the display panel; frame memory means temporarily storing sequentially received video signals and outputting a video signal from the prior frame; and means for converting video signals receiving the sequentially received video signals and the video signal from the prior frame, looking up a look-up table, and correcting and outputting a liquid crystal driver signal to eliminate gradation offsets based on hysteresis in the display panel.
In this conventional technology, a gradation level higher than the gradation level of the video signal is displayed (hereinafter referred to as overshooting) to eliminate gradation offsets causes by hysteresis in the display panel. However, the display panel itself does not generate gradation offsets due to hysteresis, so there is no need to provide overshooting as shown in FIG. 4 from the conventional technology. Thus, correction cannot be provided for luminance surpluses and deficits caused by response delays in the display panel.
Also, in the conventional technology described above, video signal converting means must access the look-up table for each image element in each frame. As the display screen increases in size or resolution, the information in the look-up table increases and the time required to convert a single frame of video information increases. As a result, the display device will not be able to provide fast response times. For example, to perform 256-level displays, correction values must be determined for 256×255=65280 possibilities. Assuming an 8-bit look-up table, 256×255×8=510 kbits of memory would be required. If a single frame contains 1280×1024=1587.2K pixels, there will be 4761.6K image elements (since each pixel is formed Red, Green, and Blue image elements). In other words, for each frame, the look-up table must be accessed 4761.6K times.